Get rid of unwanted information from serial.read()

Hardware Arduino GSM Shield
4

Basically you'll read all characters sent to you by the gsm.

+CMT: "+6XXXXXXXXXXX","","16/05/18,15:36:07+32"

Until you get the first character of the message your interested with then start storing them.

if(SIM900.available() >0)
  {
    incoming_char=SIM900.read(); //Get the character from the cellular serial port.
    Serial.print(incoming_char); //Print the incoming character to the terminal.
}